When organs of the body are formed, they develop in neatly organized arrays. Often, cell types are separated by connective tissue called basement membranes. In skin, for instance, the superficial layer of epidermal cells adheres to the underlying basement membrane. This skin basement membrane acts as a barrier between the epidermal cells on the outside, and the dermal cells underneath. A similar arrangement of cells occurs in the lining of the gut and in the oral cavity.
Basement membranes have been implicated in the growth, attachment, migration, repair and differentiation of their overlying cell populations. Three layers have been defined in basement membranes: a) the lamina lucida, an electronmicroscopically clear region in close approximation to the overlying cells; b) the lamina densa, an electron dense region of 20-300 nm in width; and c) the sublamina densa which contains anchoring fibrils, microfibrillar bundles and collagen fibers.
Many epithelial cells interact with the underlying extracellular matrix, a network of proteins to which cells attach, via a junction called the hemidesmosome (Staehelin, (1974) Structure and Function of Intercellular Junctions, Department of Molecular, Cellular and Developmental Biology, University of Colorado, Boulder, Colo., 191-283). The hemidesmosome, with its anchored structures including intermediatei filaments and anchoring fibrils, forms an adhesion complex. The purification of adhesion-facilitating proteins has remained elusive. Burgeson et al (PCT Applications No. WO92/17498 and WO94/05316) disclose a protein, kalinin, which is said to facilitate cell adhesion to substrates; however, this material is apparently inactive with respect to hemidesmosome formation.
When cultured on tissue culture plastic in vitro, most epithelial cells do not assemble bona fide hemidesmosomes despite the fact that they appear to express all of the necessary plaque and hemidesmosomal components. The 804G and NBT-II rat bladder carcinoma cell lines were recently discovered to have the ability to readily assemble hemidesmosomes in vitro under standard culture conditions (Riddelle et al., (1991) J. Cell Biol., 112:159-168; Hieda et al., (1992), J. Cell Biol., 116:1497). It has also been reported that substratum-induced staining by anti-hemidesmosome antibodies is greatly diminished in 804G cell cultures that enter in vitro wound sites (Riddelle et al., (1992) J. Cell Sci., 103:475-490).
As described in Langhofer et al. (1993) J. Cell Sci., 105:753-764) and in copending U.S. application Ser. No. 08/042,727, hereby incorporated by reference, when epithelial cells unable to themselves form hemidesmosomes are plated on the cell matrix secreted by 804G cells, hemidesmosome formation is induced. In addition, copending U.S. application Ser. No. 08/151,134, hereby incorporated by reference, teaches that a soluble factor produced by 804G cells can also induce attachment and hemidesmosome formation in cells contacted with the factor. Further, this pending application discloses that the 804G factor is comprised of protein components having significant similarity to human merosin, a laminin A isoform, and to Drosophila laminin A. Copending U.S. application Ser. No. 08/152,460, also incorporated by reference, discloses the enhanced growth of pancreatic endocrine precursor cells plated on the 804G matrix.
Any medical device, including indwelling catheters and colostomy tubes, which breach the skin for an extended period of time will result in inflammation and/or infection. It would be particularly desirable to coat the surface of these devices with epithelial cells prior to or after insertion into the skin to prevent these undesirable processes. It would also be desirable to coat surgical meshes with epithelial cells for use in skin allografts. In addition, periodontitis, a severe form of gum disease resulting in destruction of gum tissue epithelium and bone erosion, would be amenable to treatment with dental abutment pieces coated with epithelial cells. This would promote reattachment of detached gum tissue to the tooth surface.
The maintenance of tissues and organs ex vivo is also highly desirable. Tissue replacement therapy is well established in the treatment of human disease. For example, around 42,000 corneal transplants were performed in the United States in 1993. Human epidermal cells can already be grown in vitro and used to populate burn sites and chronic skin ulcers. However, many primary cells and tissues are difficult to establish in vitro on normal tissue culture plastic. Although this problem is partially alleviated by the use of extracellular matrix-coated cell supports, this is only a temporary solution.
Thus, there is a need for trans-epithelial appliances capable of stimulating epithelial cell attachment and spreading and for a composition capable of supporting the viability of tissues and organs maintained ex vivo. The present invention satisfies these needs.